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1
The Benefits of Three Columbia Slough Restoration Projects on the
Natural and Urban Environment.
Chris Brown, Arielle Glade, Mary Head, Joe Miller and Brian Thatcher
Abstract:
We sampled three different restoration projects; the Whitaker Ponds, the Vanport
Wetlands and the Section 1135 Project, to determine what ecological and community
benefits restoration is having on the slough and the local community. The Whitaker
Ponds, once a junkyard, has been restored to a semi-pristine state and now acts as a
community environmental learning center to create awareness of watershed importance.
The Vanport wetlands is a young mitigation project that has already shown to aid in
wildlife recovery and species diversity. The $4.5 million section 1135 restoration project
consists of several components to focus on system restoration. Each of these projects has
shown to be successful early on, and a more concerted effort to collect quantitative data
will help in steering future projects.
Key Words: Columbia River Slough, ecosystem, wetland restoration, urban ecosystems
2
Introduction
The Columbia River Slough is a heavily industrialized and highly impacted area
located in north Portland, Oregon. Within the past decade the value of its natural state
has been realized, and efforts are being made to restore various areas. As land becomes
available, the regional Metro government and other government agencies are acquiring
lands to use as open space, recreation, and wildlife habitat (personal communication, Jay
Mower, CRS watershed council). Currently, there are dozens of restoration projects by
various government agencies, non-profit groups and volunteer workers. However, there
is no concise relationship between these projects, nor any methodology to measure the
projects’ effectiveness.
This study investigates three separate restoration projects, the Whittaker Ponds,
the Vanport wetlands, and the Columbia Slough Section 1135 Project, to determine the
benefits that restoration has had on the urban community, wildlife habitat, and wetland
revival, respectively. The goal of the study was to collect quantitative and qualitative
data to support our hypothesis that these projects are benefiting both the urban and
natural environments. Since most of these projects are fairly new, there is a lack of
quantitative data available, however there is great enthusiasm in the community resulting
in an abundance of qualitative data.
History and Background
The Columbia Slough is part of a 61 square mile watershed that consists of
wetlands, lakes and sloughs in the north part of Portland, Oregon. The slough is an
eighteen-mile waterway that parallels the Columbia River and flows west from Fairview
Lake near the town of Gresham, to its confluence with the Willamette River in Portland.
3
The vertical drop in river level over this distance is less than 1 inch (Personal
Communication, Sue Barthow, Nov. 2002). The slough was a natural flood plain
absorbing the flood waters from the Columbia River, but people have induced changes to
the lands near the slough altering its function as a natural floodplain to a completely
managed drainage canal (Center for Columbia River History [CCRH], 2002). Since the
slough was a floodplain, periodic flooding produced rich soils over time giving life to
many plants and animals, and eventually drew human settlement to the area. In the early
1920's, levees were constructed to prevent seasonal flooding and the waterway was
transformed into the channelized and highly managed system now known as the
Columbia Slough. With the elimination of yearly floods, farming, industrial and
residential development flourished. As Collins et. al. point out, urban ecosystems,
including the slough, are dynamic and changing (2000). The slough is considered a
habitat patch but human changes have removed natural succession with flood control.
People are now introducing a means to enhance biodiversity and succession with
restoration.
Today, settlement among the Columbia Slough Watershed has led to over
158,000 residents, 4,200 companies, 24,000 homes, 3,000 businesses, 6 golf courses, 3
Interstate Freeways, a horse track, motor vehicle raceway and the Portland international
airport. 3 drainage districts (for flood control) and 25 miles of levees protect over $10
billion worth of property, 2 sewage treatment plants, and is home to 1/10 of all the jobs in
Oregon. The Slough currently drains more than 34,000 acres of residential, commercial
and industrial lands. More than 200 industrial, business, agricultural and recreational
facilities border the Slough (CCRH). Many of the banks are steep and eroded.
4
Undeveloped areas along the Columbia Slough are classified as Flushed Slough and
Scrub-shrub. This means that the banks are covered, for the most part, with blackberries,
willows, and shrubs. These are non-native plant species that out-compete native species
(Community Watershed Stewardship Program [CWSP], 2002). Even with these
environmental impacts, the slough is still one of Portland’s largest open spaces and
wildlife habitat resources. River otters, beavers, coyotes, and bobcats live along the
banks and cougars have been seen around the slough. Cover and feed is provided for
over 120 bird species by the riparian areas and wetlands. Many tree species such as the
black cottonwood, ash and willow offer a shady screen from nearby industrial areas
(Portland BES, 2002).
Years of filling and diking have created two distinctly different sections of the
slough. The lower slough extends from the Willamette River to the Peninsula Canal
(about NE 13th Ave). One contiguous stretch, the lower slough offers high-quality canoe
and kayak recreation to urban paddlers. Daily tidal influences may change water levels
as much as three feet in this portion of the Columbia Slough. The upper slough
continues eastward to Fairview Lake, but consists of long, narrow pond- like segments
separated by road crossings and connected only by culverts that restrict small boat traffic.
Storm runoff and springs provide much of the flow for the upper reach (Portland BES,
2002).
The climate around the slough consists of wet winters and dry summers. In the
spring, the snow melts heavily in the Cascade Mountains located to the east and drains
into the Columbia River sending some water to the slough.
5
Each year more than 13.7 million people and over 275,000 tons of freight come
through the watershed. Impacts from 150 years of development have left a legacy of
environmental problems in the Slough: contaminated fish and sediment, diminished
wildlife habitat, and water pollution from both point and non-point sources (Columbia
Slough Watershed Council [CSWC], 2002). Both sections of the slough face threats to
water quality. Until recently, thirteen combined sewer outfalls (CSO’s) empty diluted,
untreated sewage into the lower slough whenever heavy rainfall overloads the City's
sewer system. Along with the trouble of these CSO’s is the landfill area, encircled by the
Columbia Slough. It was once a wetland, home to an abundance of wildlife, plants, and
fish. Through the years, industrial growth in the St. Johns area and growth of the landfill
have altered this ecosystem. The high contamination levels in the Columbia Slough are
partly due to waste disposal at the landfill. Storms also wash pollutants from nearby
streets and industrial developments into the slough. The upper slough is further polluted
by septic tank and cesspool effluent that enters the groundwater in mid-Multnomah
County, emerging from the springs that feed the slough (Wells, 2002).
A great success happened for the slough in October 2000, the City of Portland
Bureau of Environmental Services completed its "Big Pipe" project and sewage stopped
flowing in to the Columbia Slough for the first time in a century. The elimination of
CSOs from the Slough will greatly increase the health of the waterway (CSWC).
Study Sites
Three sites were sampled for qualitative data to answer our question of restoration
efforts and benefits to the urban environment. The Whittaker Ponds were an old
6
junkyard restored in a collaborative effort by city agencies, non-governmental
organizations and volunteers. The Vanport Wetlands have had a large amount of
revegetation and invasive species removal, and have subsequently seen an increase in
wildlife populations. The section 1135 project is a large and multi-dimensional
restoration project involving federal and state agencies. It focuses on wetlands as a
system and encompasses various levels of restoration types, including the dredging,
formation of wetland benches and revegetation. This paper will focus on the wetland
benches and revegetation of the section 1135 project to indicate effectiveness to
ecosystem health.
Whittaker Ponds
In order to improve wetland quality through
community restoration projects, public
awareness and environmental education are
essential. Environmental education, in
particular, is a way to strengthen environmental
stewardship within communities. By teaching students about the important ecological
roles of wetland and riparian environments, the surrounding community will have a better
appreciation for the restoration project, and the restoration project will have a greater
chance of success (Lundmark, 2001). Whitaker Ponds is an example of how community
participation and environmental education go hand in hand with restoration projects.
Over the years, several educational projects have developed at Whitaker Ponds, bringing
thousands of students to the site.
Source: Columbia Slough Watershed Council Website
7
Whitaker Ponds is a 12-acre site with two ponds. Formerly part of a larger system
of lakes and ponds on the Columbia Slough, the ponds have been separated due to
industrialization of the surrounding area. The land was first purchased by the City of
Portland and Metro. Since this purchase, Portland Public Schools has also purchased and
incorporated land to the restoration site. Whitaker Ponds now serves as an environmental
learning center for the local community and school district. The partnership between the
city and school system has proven to be a valuable asset to the area.
Purchased by Metro in the early 1990’s, the Whitaker Ponds site was a junkyard.
Contamination included stormwater discharge, oil, and runoff from Columbia Boulevard.
The restoration process included the removal of garbage, planting native vegetation, and
building a small water treatment and testing center adjacent to the ponds (CCRH, 2002).
This process has involved many people from the surrounding community and schools.
Restoration at Whitaker Ponds has been about both repairing the surrounding ecosystem
and increasing the community’s knowledge base about the ponds. The largest step
towards involving the community started with the completion of the Whitaker Ponds
Environmental Learning Center. The learning center has become a significant point of
activity on the Columbia Slough.
In 1999, the EPA gave the Multnomah School District “Turnaround School” a
grant to help in the restoration project at Whitaker Ponds. Through this grant, at-risk and
expelled students learned about the restoration process. The students “plant trees,
monitor wildlife, implement salmon recovery, remove blackberry bushes, plant native
willows, build nature paths, and implement water quality testing (EPA, 2002).”
8
In 2000, local high school students established 11 permanent monitoring plots to monitor
native plant growth at sites that were planted from 1995 to 1997.
The Environmental Learning Center also has a variety of educational programs available
to teachers who want to bring students to the site for a field trip. The field trips teach
children about restoration through activities similar to those of the “Turnaround School”
(Sustainable Portland, 2001).
In 2000, the City of Portland’s Bureau of Environmental Services (BES)
Revegetation Program and community volunteers planted 3,000 plants and shrubs around
Whitaker Ponds. Bi-annually, the BES and the Columbia Slough Watershed Council
hosts an event called “Soup on the Slough” at the Whitaker Ponds. At this event,
community members are invited to lunch or dinner to talk about the restoration projects
taking place at the site and to share their concerns and perspectives about slough-related
topics (CSWC Annual Report, 2000).
Another benefit of restoration on the ponds is an experiment to reduce pollution
from runoff from Columbia Blvd., located 300 yards uphill of the ponds (see figure 1).
Pollution from the runoff includes oil,
industrial wastes, and tire dust. Water
flows into a concrete- lined retention tank
(donated by a local landowner), where
solids settle out. Water then flows into a
pond located downhill from the retention
tank. Water is stored in this pond where
a portion evaporates and the rest seeps
9
through the ground into a second pond. This process is repeated a total of 4 times. The
lowest pond (not Whitaker) is covered with Duckweed, a fairly recent change, and
though no quantitative data is available, water in the Duckweed pond is significantly
cleaner with vibrant plant growth and a flourishing insect population (Personal
Communication, Sue Barthow, Nov. 2002). A restoration project in the Everglades of
Florida indicates that the presence of Duckweed and insects are indicators of a healthy
ecosystem (Levin, 2002).
Though the ponds are relatively small, a study by Oertli et. al. concludes that
species diversity is not a function of pond size, and that size showed only a minor
relationship with species richness (2002). This study helps to justify the effort of
purchasing and restoring small areas.
Without the organized participation of community and schools, Whitaker Ponds
would not have the level of information and restoration completed that it has today.
Through the aid of local scientists and environmentalists, wetland restoration has become
an exciting and fun topic for school children. The Learning Center at Whitaker Ponds
serves as a tool for the entire Columbia Slough.
Vanport Wetlands
The 91-acre sites occupied
by Vanport wetlands have had
many faces over the years:
� Prior to the 1920’s the site
was actually Force Lake,
Source: Port of Portland An aerial view showing the locations of the old radio towers on the newly named Vanport wetlands.
Aerial view of Vanport wetland site (Source: Port of Portland website)
10
named after a family that settled the area.
� In 1920 the Penninsula Drainage District drained Force Lake and the surrounding
floodplain in order to develop more land for farming.
� The KGW radio towers where built on the land in the early 1920’s, hence the name of
“radio tower site” adopted after the great flood of 1948 that was the demise of the
Vanport area.
� The land was farmed continually until 1965 at which point the land was abandoned to
be taken over by invasive plant species primarily reed canarygrass, thistle, blackberry and
nightshade
� In the 1990’s the Port of Portland permitted for the filling of a wetlands near the
airport. When the Port can’t avoid the filling of wetlands they buy proportional land in
the same watershed restoring it to natural wetlands.
� The Port contracted with natural resource agencies and interested watershed groups to
finally decide on a site to purchase. In 1999 the Port purchased the radio tower site and
the mitigation process began.
The Port of Portland has an environmental plan to create as much wetland as it
destroys. In other words, if some wetlands are destroyed in the process of a project, then
the Port will purchase a proportional or greater piece of land in the same watershed for
restoration. A direct result of this plan was the purchase of the KGW Radio Tower site
later known as the Vanport wetlands. The Port of Portland decided that it was necessary
to enlarge part of the Portland airport, which resulted in the loss of about 18-acres of
wetlands. In response to the impending loss the Port hired an environmental research
agency to find a comparable wetland in the Columbia Slough watershed for purchase.
11
KGW radio station basically neglected the 91-acre site allowing invasive vegetation
to begin taking over the land. The majority of the land was covered by reed canarygrass
with other densely populated areas of thistle, blackberry, and nightshade. The invasive
vegetation was so dense that it smothered nearly all other plant species in the wetland
causing virtually no diversity. The result is a limited variety of wildlife that will use the
wetland due to limited food sources.
The goal of the mitigation plan is to increase diversity of plant and wildlife habitat
on the site by establishing a more diverse native-dominated wetland habitat with a
surrounding vegetative buffer (Port of Portland, 2000). The objective for restoration of
the Vanport wetlands is unlike most restoration projects in that the intentions are not to
bring the area back to its original state. The intentions are to create new wetlands to
enhance habitat for wildlife and native vegetation. After the Port of Portland acquired the
land in 1999 a plan was developed to rid the new wetlands of invasive plant species
through the following: mowing, disking, reseeding with native vegetation, and finally
flooding the land to further inundate the invasive vegetation with stress. Prior to
flooding the wetlands an earthen dike had to be built around the wetland to aid in flood
control or more accurately to keep from flooding expo road. Another earthen project
was to reconfigure the existing ditch system to a more natural meandering flow.
The site restoration is relatively new, which means solid data on how well fauna
and flora are coming back is not readily available. However, according to the Port of
Portland’s website the ducks and geese are flocking to the new wetlands. The wildlife in
general has been coming back steadily and the replanting of good wetland vegetation will
only enhance the waterfowl conditions further. According to a Carrie Stevenson of the
12
Port of Portland the waterfowl have been thriving especially well now that the wetland is
flooded nearly year around. She went on to say that it’s not uncommon to see hundreds
of Canadian honkers and ducks using the area. New sightings of Pintail, Green Wing
Teal, Canvasback, and Northern Shovelers are becoming more common than not.
Many different birds of prey, such as American kestrel, bald eagle, red-tailed hawk,
osprey and great horned owl have been observed frequenting the wetlands. Several other
species of birds have been observed in the area no doubt as a result of the increased
waterfowl in the wetlands. The wader and shorebird types have increased rapidly in the
wetland, probably due to the muddy wet edges of the swale that make for perfect
foraging. Some of the more common waders and shorebirds to the wetlands are the
common snipe, greater yellowlegs, long-billed dowitcher and sandpipers. The great blue
herons as well as killdeer are frequently observed wading along the swale. With the
increase in use by waterfowl and various bird species nesters have been observed to be
using the wetland during the spring months. The nesters where observed to be mallards,
killdeer, marsh wrens and cliff swallows (Port of Portland, 2002).
According to Stevenson, the battle with reed canarygrass and Himalayan
blackberry has been very successful thus far. The port battled the invasive vegetation
with the use of herbicides followed by disking the ground to further disrupt the plant.
The result of a successful wetlands (Source: Port of Portland website).
13
The battle against the Himalayan blackberry has been especially successful by the
means describe above. Unfortunately, the Port was unable to flood the entire wetland due
to lack of rain, which has
slightly stymied the battle
against the reed canarygrass.
However, Stevenson went on
to say that the diversity of
vegetation is already very
noticeable with the
emergence of bulrush,
spikerush, burreed and other intentionally planted or seeded vegetation.
The building of the earthen dikes had many purposes, one of which was to
prevent the flooding of expo road
the other was to allow for flooding
of the wetland. The earthen dikes
have obviously been built to
maintain some control over the
flooding process, which is further
controlled through a single pump
station from the Columbia slough. The reconfiguration of the ditch has resulted in a more
natural meandering swale like system.
The building of the meandering swale and the earthen dikes where performed using heavy equipment (Port of Portland website).
The Port’s Carrie Stevens plants twinberry shrubs on the bank of the earthen dike in January 2002 (Port of Portland website).
14
Section 1135 Project
The 1135 project, named after the U.S. Army Corps of Engineers (USACE)
Section 1135 Restoration Program, is a multi-agency project consisting of several
components along a 7.5 mile stretch (see map 2) of the slough. The nearly five million-
dollar project is 75% funded by the USACE and 25% funded by the city of Portland BES
(“Slough News,” 2002). It consists of several components, including:
1. Creating meandering channels and wetland benches. 2. Revegetating the new benches and controlling invasive non-native plants. 3. Replacing ineffective culverts in Buffalo and Whitaker slough. 4. Creating a 9-acre wetland to provide wildlife habitat and filter storm water
(USACE Columbia Slough Section 1135 Restoration Project Report, 2001).
This collaborative effort is aimed at the ecological system instead of at a single
location. While this is much more expensive, the long-term benefits should return a
healthier ecosystem.
Multnomah County Drainage
District #1 (MCDD #1) is responsible for
dredging channels and building benches.
Due to the steep banks and narrow channel,
there is little emergent marsh habitat
(USACE Section 1135 Restoration Report,
2001). This would involve dredging the slough to a designed depth and placing material
along the banks to create wetland benches and meandering channels (Fig. 2). The
Portland BES is planting emergent plants along these benches. This combined effort will
reduce sedimentation from runoff, provide erosion control and reduce water temperatures
(Lyn Barlow, Personal communication, Nov. 2002), all necessary components of
Map 2--Section 1135 project restoration sites (Source: USACE project report)
15
healthy salmon and steelhead habitat. The primary goals of the revegetation (BES
Watershed Revegetation Program Monitoring and Documentation Protocol) are:
1. Increase native tree canopy, shrub cover, and herbaceous cover
2. Increase shade over surface water. 3. Increase native plant diversity and structure for
wildlife habitat. 4. Reduce erosion by stabilizing soils with native
plantings and bioengineering. 5. Evaluate overall plant survival, mortality, and
vigor by project site to indicate the need for planting treatments.
6. Reduce non-native weedy species.
Since this project began in July 2002, no
quantitative data has been produced to measure how effective the wetland benches and
revegetation has been. Subsequently, there is little baseline data to compare with
(Personal Communication, Lyn Barlow, Nov. 2002). However, the Portland BES has
developed certain guidelines it will use to monitor the revegetation. One is a quantitative
measurement and the other utilizes photo monitoring.
Quantitative Data Analysis
Portland BES uses a simple equation to calculate means and extrapolation of plot means
to generate per-unit area averages:
Planted TPA=T/nA
where: Planted TPA= planted trees per acre T= total number of trees found on all plots n= total number of plots A= area of plot in acres
Survival percentages are calculated as the proportion of surviving planted trees or shrubs
on plots divided by the total number of trees or shrubs originally planted on plots (BES
Figure 2--Wetland bench design diagram (Source: USACE project report)
16
Monitoring and Documentation Protocol). This simple formula will give a general
indication of how well revegetation is taking hold of the wetland benches.
Photomonitoring
Photomonitoring is one of the most basic monitoring techniques, however photographs
taken over a number of years are a valuable tool of evaluating plant progress. The two
types of photographs used in this evaluation method are a general view (including
features and landscapes) and close-ups.
• Feature photos: a general view photograph is taken along a transect in both
directions. For example, plots are set up to monitor changes of a stream bank. A
prominent landmark is chosen and two stakes about 40 feet apart are used to
center the photos. A photo identification label is used to ensure photos of the
same stream segment are taken and the dates kept in order.
• Landscape photos are an overview of the area showing the feature and its
relationship to the surrounding area. These photos are used to show the area of
the same section of stream of feature photos.
• Close-up photos show specific characteristics of an area, such as emergent
wetland vegetation, soil surface or ground coverage. Close ups photos are taken
from points permanently located to give as much information of change as
possible.
Sites are monitored several times within a 5-year period, depending on the type of
vegetation planted.
Discussion & Conclusions:
17
Current data collection has proven that the water quality in the slough has gone up
(CCRH, 2002), however it is insufficient to judge how well restoration as a whole has
benefited the slough. However, the qualitative data collected through interviews,
informal discussions and prior work has proven that the slough is a more productive
ecosystem. The lack of baseline data collection prior to the beginning of many projects
will inhibit the measurement of change over time, and current data collection should be
increased assess what types of restoration are more effective than others.
The three projects discussed in this paper are fairly typical of many of the other
projects occurring within the slough. They are a representative sample of how restoration
projects are benefiting this urban ecosystem. The number of government agencies
involved in restoring the slough is indicative of the importance of the area. While it will
continue to be intensely managed for anthropogenic use, natural flora and fauna
populations can recover and play a role in the ecosystem. The Whitaker Ponds brings the
community together and educates the next generation to value the area as an integral part
of the urban ecosystem. The Vanport Wetlands, though only recently restored, has seen a
marked increase in bird populations. The natural removal of an invasive species by
flooding is an alternative to labor- intensive non-native vegetation removal by hand.
Replanting produces emergent wetland species that soon become self-supportive. The
section 1135 Project is an example of how the financial sources of government agenc ies
can make wide sweeping changes. This project will reduce the listed TMDL’s of section
303(d) of the clean water act. These projects, with its many separate aspects, combine to
restore the ecosystem back to a system, where all the parts work together. These sampled
18
projects support our hypothesis that restoration in the Columbia River Slough is
benefiting the urban and natural environment.
Recommendations:
Dave Hendricks, MCDD #1 Operations Manager, says of restoration:
“(W)e can restore all the habitat we want to, but without the proper maintenance,
without people overseeing and managing newly planted area, it’s going to
deteriorate as fast as we restore it. And, this is especially true for wetland
creation—something we do a lot of in the Columbia Slough Watershed (CCRH,
2002).”
Within the past ten years restoration projects have become very common.
Government agencies from the federal down to the local level are realizing the value of
the slough, but there is currently little cooperation from one restoration site to the other.
There is no one source documenting the various projects, therefore it is difficult to plan
restoration as part of a system instead of as individual components. A provision should
be in place to document what is occurring, where, at what time and its details. This will
allow the people involved with restoration to concentrate efforts to include a range of
components, much like the Section 1135 Project, only on a larger scale.
Volunteers have been an integral part of restoration, and the slough attracts many
educators and businesses. People involved range from neighbors to academics to large
business owners (personal communication, Soup on the Slough, Nov. 2002). Clearly the
benefits of the slough as a healthy ecosystem are benefiting the local community, and
vice versa, and while there is always room for more help, local organizations are doing a
good job of keeping the community involved.
19
Works Cited
BES Watershed Revegetation Program Monitoring and Documentation Protocol (2002. City of Portland Bureau of Environmental Services Watershed Revegetation Program, unpublished document.
Center for Columbia River History, (2000). The Future of the Columbia Slough.
Retrieved November 13, 2002, from http://www.ccrh.org/comm/slough/class2/future.html.
City of Portland, Bureau of Environmental Services, (1991). Basin Focus:
Columbia Slough. Retrieved November 13, 2002, from http://www.ccrh.org/comm/slough/primary/basin.htm.
City of Portland Bureau of Environmental Services, 2000 Community Watershed
Stewardship Projects Annual Report. Collins, J.P., Kinzig, A., Grimm, N., Fagan, W., Hope, D., Wu, J., and Borer, E. (2000).
A New Urban Ecology: Modeling human communities as integral parts of ecosystems poses special problems for the development and testing of ecological theory. American Scientist (88), p. 416-425.
Columbia Slough Section 1135 Restoration Project Ecosystem Restoration Report and
Environmental Assessment (2001). U.S. Army Corps of Engineers, Portland Branch
Columbia Slough Watershed Council, (2002). About the Watershed. Retrieved
November 13, 2002, from http://www.columbiaslough.org/watershed.html.
Environmental Protection Agency (1999). Grants, accessed on 11/20/02,
www.epa.gov/enviroed/grants/or.htm. Levin, T. (2002). Reviving the River of Grass. Audubon Society Magazine, July-Aug.
(p. 54). Lundmark, K. (2001, August). Keeping Track of Wetland Restorations. BioScience, 696-
699 Oertli B. ; Juge R. ; Cambin D. ; Lachavanne J.-B. ; Joye D.A. ; Castella E. (2002). Does
size matter? The relationship between pond size and biodiversity. . Biological Conservation 104(1). p. 59-70
20
Port of Portland (2002) Columbia Slough Mitigation Site, November 2002, http://www.portofportland.com/pop/Environmental/environ_miti_home.htm http://www.portofportland.com/pop/Environmental/environ_miti_sites.htm#Vanport%20Wetlands%20Site http://www.portofportland.com/pop/Environmental/pdf/RadioTowers_Update_1
Sustainable Portland, 2001, Green Pages, accessed on 11/20/02,
www.sustainableportland.org/GreenPages/Classrooms.htm. Slough News (2002) Newsletter of the Columbia Slough Watershed Council, 3(2). Wells, Scott A, (1997). The Columbia Slough. Retrieved November 13, 2002.
http://www.ce.pdx.edu/~scott/pubs/slough/cop-public-rpt.htm.